Pull different EMSDK versions according to build type

.github/workflows/build_libzim_wasm.yml

@@ -42,6 +42,7 @@ env:
   DISPATCH_TYPE: ${{ github.event.inputs.buildtype }}
   GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
   SSH_KEY: ${{ secrets.SSH_KEY }}
+  BUILD_TYPE: ${{ github.event.inputs.buildtype }}
 
 jobs:
   build:
@@ -51,7 +52,13 @@ jobs:
     - uses: actions/checkout@v3
     # Customizes the Emscripten docker container via the Dockerfile in this repo
     - name: Build the Docker image
-      run: docker build -t "docker-emscripten-libzim:v3" ./docker
+      run: |
+        if [[ $BUILD_TYPE =~ 'source' ]]; then
+          BUILD_VERSION='3.1.12'
+        else
+          BUILD_VERSION='3.1.41'
+        fi
+        docker build -t "docker-emscripten-libzim:v3" ./docker --build-arg VERSION=$BUILD_VERSION
     # If we're building release version
     - name: Build release from libzim binaries
       if: github.event_name == 'pull_request' || github.event_name == 'push' || github.event.inputs.buildtype == 'release'

docker/Dockerfile

@@ -1,5 +1,6 @@
 # Docker image suitable to build libzim & kiwixlib with emscripten
-FROM emscripten/emsdk:3.1.41
+ARG VERSION
+FROM emscripten/emsdk:${VERSION}
 
 # Install build tools
 RUN apt-get update && apt-get install -y --no-install-recommends wget ninja-build pkg-config python3 autopoint libtool autoconf patch g++ locales curl git \